Related (on a different site): How does one typically determine the energy and force in a foot stomp?

I recently got a knee injury and was trying to understand when it was safe to continue to practice. Disconcertingly enough, my doctors and physical therapist seemed to have only a vague idea of what kind of stress martial arts apply on the body or exactly how much force kicks apply to the knee.

I do realize that this is a weird thing to know, but it seems like it would be very hard to know exactly when it was safe to go back without knowing that. Indeed, the assessment to decide whether or not to discharge me from physical therapy was heavily oriented towards non-martial-arts activities.

Is there a mathematical model of some kind that shows exactly what kind of force is applied by various activities? For example, during a spinning hook kick, how much lateral force is applied to the planted foot?

How would I calculate something like this?

Note: I'm not soliciting medical advice, as I do realize that that is off-topic here. Rather, I'm asking about the mechanical force involved "in general."

  • wouldn't this be a physics question?
    – Daniel
    Commented Mar 22, 2019 at 9:01
  • @Daniel It’s on topic on both sites I think. Commented Mar 22, 2019 at 12:57
  • I don't see how knowing the force vector will help you. Do you somehow know what force you can sustain?
    – mattm
    Commented Mar 22, 2019 at 18:00
  • @mattm That's a good question, actually. That would be a very worthwhile follow-up question, but that would probably be more appropriate for Medical Sciences SE or Biology SE than for here. Commented Mar 22, 2019 at 18:22

1 Answer 1


If you want mathematical models for forces on human joints, I think the place to look is biomedical engineering. I doubt they have models specifically for tae kwon do, but they should have validated models for forces on joints, and perhaps even instrumentation on joint replacements. It should give you a place to start.

In your linked question, there is actually no modeling of forces for striking. I suspect this is because it is very hard to instrument someone's joints, so the best you can do is instrument externally on the striking surface.

I think you overestimate how much is known about recovery from knee injuries. In 2013, a new knee ligament was discovered.

Last month, knee surgeons from the University Hospitals Leuven in Belgium announced that they had found a new knee ligament, one that had not previously been specifically identified despite untold numbers of past knee dissections and scans.

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